Summary Air Canada Flight 163 (ACA163), a Boeing 767-200, was inbound to Vancouver from the northeast and vectored to Runway 26R. At the same time, Singapore Airlines Flight018 (SIA018), an Airbus A340-300, was inbound from the southwest and vectored to Runway 26R. When ACA163 was on right base and descending from about 4800feet to 3000feet, SIA018 was established on left base and level at 4000feet. During this turn onto final, a loss of separation occurred and both aircraft closed to within 600feet and 1nautical miles of each other before the required separation was restored. Ce rapport est galement disponible en franais. Other Factual Information ACA163 first contacted Vancouver's arrival low controller at 1102:48 Pacific daylight time1 and reported out of 6000feet, descending to 5000feet. At that time, the aircraft was turning left to a heading of 080 and descending at about 1000feet per minute (fpm) while maintaining a speed of about 250knots. The arrival low controller cleared ACA163 to maintain 3000 feet and cautioned the crew about turbulence because they would be following a heavy aircraft. Figure1. Relative positions after initial contact with the arrival low controller. The stars show each aircraft's position. The dotted lines show each aircraft's respective previous track. SIA018 checked in with the arrival low controller about 20seconds later, when their aircraft was in a descent and approaching 5000feet. The controller acknowledged the check-in and cleared the aircraft to continue its descent to maintain 4000feet on a heading of 070. The relative positions of the two aircraft after this initial contact with the arrival low controller are shown in Figure 1. At 1103:31, the controller directed ACA163 to turn right to a heading of 170. Nine seconds later, the controller directed SIA018 to complete a left turn to a heading of 350. Once established on this reciprocal track, the combined closing speed of the two aircraft was about 480knots (8 nautical miles [nm] per minute). At 1104:06, the arrival low controller vectored ACA163 right to a heading of 230 and cleared the aircraft for an instrument landing system (ILS) approach to Runway26R with a speed restriction to maintain 170knots. When ACA163 received the approach clearance and associated speed restriction, the aircraft was descending through about 4800 feet and maintaining a speed of about 250knots. ACA163 commenced a right turn and began to reduce speed to meet the restriction; during that manoeuvre, the aircraft's rate of descent dropped to about 450 fpm. Figure2.Relative position of both aircraft during the early stages of ACA163's turn to final. The two aircraft closed to about 3.3nm and were still converging at a rate of about 8 nm per minute when the controller directed SIA018 to turn to a heading of 290 at 4000feet. (See Figure 2.) He then directed ACA163 to expedite its descent down to 3000feet for traffic. On receipt of the direction to expedite descent, ACA163's rate of descent increased to about 1000fpm, the turn radius tightened, and the speed remained at 170knots. A loss of separation occurred when the two aircraft closed to within 1 nm and 600feet in an area where 3nm horizontal or 1000feet vertical separation was required. Separation was re-established when ACA163 reached the cleared altitude of 3000feet. SIA018 subsequently reported the airport in sight and was given an amended clearance to conduct a visual approach to Runway26L. ACA163 completed the ILS approach to Runway26R. Each aircraft was fitted with a traffic alert and collision-avoidance system (TCAS). Neither crew reported or responded to a TCAS traffic alert or resolution advisory, and crews of both aircraft had reported the opposing traffic in sight. Nav Canada's primary role is to ensure safe and efficient movement of aircraft within Canadian airspace and international airspace for which it has accepted responsibility to provide air traffic services. As part of their functions, Nav Canada's air traffic controllers are required to ensure adequate separation is maintained between aircraft. Specific separation standards vary and are detailed in the Canadian Aviation Regulations. To maintain appropriate separation, controllers must plan, take appropriate steps to execute the plan, and monitor the results of their plan. Any breakdown in planning, execution, or monitoring functions is considered to be an irregularity, which could lead to a loss of separation. Aircrew and controllers follow standardized procedures; use of such procedures reduce the requirement for detailed explanations and excessive radio communication. When on radar vectors, it is important that aircrew follow the direction of a controller to ensure the success of a controller's plan. In general, however, aircrew will only know the part of a controller's plan that is conveyed to them through the communication system. Under normal circumstances, when slowing an aircraft, there is a natural consequence that an aircraft's rate of descent will reduce. Nav Canada recognizes an increased risk in directing altitude changes while vectoring aircraft on reciprocal tracks. This type of control plan is considered by Nav Canada to be very unforgiving; it increases a controller's monitoring requirement, increases the risk of error from distraction, and makes recovery from any potential error more difficult. Examples of previous events where this type of control procedure did not work properly have been disseminated to controllers through Nav Canada's internal communication system (Air Traffic Services Bulletin - Squawk 7700 Number 9501).